In many fields of engineering a local conglomeration of completely different kinds of electrical and electronic equipment is required to exchange information which thus requires networking in a sometimes complicated manner. For instance, in motor vehicles, sources of audio signals such as radio receivers, cassette recorders or CD players require, on the one hand, connecting together and, on the other, to audio sinks such as amplifier speaker combinations. It may prove useful to also incorporate audio equipment which formerly formed a separate system, such as car phones in such a system. In addition, there is a trend towards increasingly complex control and monitoring of vehicle functions. Of the innumerable possibilities in this respect, here merely monitoring the function of external lights on the vehicle or the inflation pressure or measuring and/or controlling the engine speed or the turbocharging pressure is cited.
For this purpose extensive wiring connections are necessary between the individual components. Even when, as intended, many items of equipment and functions are controlled and handled by a vehicle computer, the problem of the many wires and the length thereof remains. Also of disadvantage is the fact that many of the known components are unable to directly communicate with each other. For instance, to prompt the audio system to output a recorded text as a warning via the speakers, in the case of a reduction in tire inflation pressure, the expense involved until now was prohibitive. A great many other examples of networking vehicle components have already been stated which, however, have only been realized in part, such as a standardized transfer of audio data, on the one hand, or control data, on the other, each via a separate network of shielded wiring. Employing a bus system, although desirable, is hampered by major difficulties as regards the necessary bus arbitration and the resulting time losses. Since users of the most different kinds have to be connected to the common bus line which is required to handle a data thruput, to transfer two-channel digital audio data in addition to control and measurement data, for example, conflicting transfer requirements can hardly be avoided.
The object forming the basis of the invention is to achieve a universal system for the exchange of audio and control data between many and varied items of electrical and electronic equipment via a bus system which is reliable, cost-effective and exceptionally powerful.
This object--as far as the method is concerned--is achieved by the features of claim 1 of the invention. The features of a bus system suitable for implementing the method according to the invention as well as a corresponding hardware interface are disclosed by claims 5 and 8.
The achievement according to the invention offers a wealth of advantages. By all items of equipment to be connected to each other being circuited in series by a single bus line, wiring can be saved and the circuiting simplified. Using fiber optic cables for data transfer achieves, on the one hand, complete freedom from noise whilst, on the other, greatly reducing weight and saving material which in vehicle applications involving the use of very many electrical and electronic components is particularly significant. Digital transfer places only minor requirements on the quality of the optical transfer medium and the electrooptical converters used and thus the costs thereof are slight. Since the transfer distances involved are short, low-cost plastic fiber optic cables can be employed. Due to the interfaces permitting standardization allowing the same type of interface module to be used, the electronics can also be realized at low cost. This eliminates complicated bus arbitration since each user has its own transmit channel and control data can be transferred monodirectional on each section of the fiber optic cable. This channel dedication permits optimum use to be made of available user channel capacity, since no capacity whatsoever must be reserved for bus arbitration. Apart from this, channel dedication permits exceptionally straight-forward user software coupling.
In the preferred embodiment of the bus system the series circuit of the users is a closed ring according to claim 10. Receiving control data can then be acknowledged according to claim 3 by a specific bit in the signal sequence being modified or removed. Since the modified signal sequence is returned to the transmitting interface via the closed ring bus system, this interface is directly informed whether its assigned control data channel is again available.
In accordance with claim 3 the AES3-1985 standard is used as the transfer format. This standard was created in coordination with the European Broadcasting Union as an internationally standardized protocol for digital audio transfer which is already used in conjunction with CD players and makes a single data channel available to the user which can be employed to transfer control data, for example. The fact that only a single data channel is available shows that this format is not actually intended for use in a bus system. The bus system according to the invention suffices with a signal channel due to the time multiplexing on the bus line. Apart from this, there is no problem in operating the bus system according to the invention with its own standard; however, using an international protocol facilitates communication with users such as CD equipment, using this protocol.
The remaining subclaims relate to further advantageous embodiments of the invention.
The invention is not only suitable for application in automobiles but also in particular in aerospace vehicles due to the low weight of the data transfer circuitry. In addition, networking stationary video, audio, telephone and data processing systems is also possible by means of the bus system according to the invention to reduce the volume of the circuit connections formerly necessary.